1. Field of the Invention
The present invention relates to an image sensor in which focus detecting pixels are arranged on an imaging plane for performing focus detection by a phase difference method, and to an imaging device including this image sensor.
2. Description of the Related Art
There is conventionally known an image sensor in which focus detecting pixels are arranged at a part of the image sensor for performing focus detection by a phase difference method. For example, Japanese Patent Laid-Open No. 2013-257494(hereafter referred to as “Patent Literature 1”) discloses an image sensor in which a right opening pixel (called R-pixel in abbreviation) to cause a subject light flux from the right side to enter the pixel and a left opening pixel (called L-pixel in abbreviation) to cause a subject light flux from the left side to enter the pixel are arranged in the horizontal direction as focus detecting pixels.
In Patent Literature 1, each of the focus detecting pixels has only one kind of characteristic in a light shielding pattern, and therefore the light shielding pattern is designed so as to obtain a high focusing accuracy near a focusing point. However, when the position of a photographing lens is significantly deviated from the focusing position, that is, in a largely-defocused state (also called a largely blurred state), the brightness pattern of a subject image is not clear and a defocus amount cannot be detected. In particular, this problem is more frequently caused for a fast photographing lens having a small aperture F-value.
If the aperture of the photographing lens is stopped down during AF operation, while the brightness pattern of the subject image can be made clear, the aperture drive takes time and an AF time becomes longer. Further, a method can be considered which solves the above problem by arranging a light shielding pattern of a focus detecting pixel for detecting the largely-defocused state and a light shielding pattern of a focus detecting pixel for detecting the vicinity of the focusing point. However, in the arrangement of the focus detecting pixels having a plurality of light shielding patterns, it is difficult to ensure an image quality performance. In particular, when the plurality of light shielding patterns is arranged for the focus detecting pixels arranged at the positions of G-pixels (pixels where green filters are arranged), correction processing of the focus detecting pixels cannot be performed.